Drilling apparatus for rotary drilling

ABSTRACT

A rock drilling apparatus for rotary drilling has a chuck which is axially movable by means of a double-acting, pressure fluid actuated feed motor. It has also a stationary chuck. The movable chuck grips a drill string when supplied with pressure fluid; the stationary chuck grips the drill string when relieved of pressure fluid. During inserting or withdrawing of the drill string, the supply conduits of the chucks are connected to either of the supply conduits of the feed motor so that, automatically, the chucks operates concordantly with the feed motor.

ilitd ties Mimi 1 swam lnventor Nils Gunner Jonsson Jakobsherg, SwedenAppl. No. 359,024

Filed Sept. 18, 1969 Patented Oct. 19, 1971 Assignee Atlas CopcoAlrtiebolag Naciia, Sweden Priority Oct. 41, 1968, Dec. 4, 1968 Sweden13476/63 and 13476/68 DRILLING APPARATUS F OR ROTARY DRILLING 8 Cs, 6Drawing Figs.

11.8. CI. I 173/149,

173/32, 173/147, 254/29, 279/4 11m. Cl E21c 1/110 Field oliSearch173/149,

[56] References Cited UNITED STATES PATENTS 931,611 8/1909 Hutchings173/149 2,830,788 4/1958 Bentley et al. 254/31 3,212,591 10/1965 Tucker173/149 3,399,735 9/1968 Ikeda 173/149 Primary Examiner-Ernest R. PurserAttorney-Eric Y. Munson 12 new PATENTEUncT 19 l97| SHEET 10F 4 NILSGUNNAR .mrmsow lNVliN'l'OR.

ERIC Y. MUNSON,

Attorney PATENTEBnm 19 Ian- SHEET l BF 4 INVIL'NTUK ERIC Y HUHSONAttorney DRILLIING APPARATUS FOR lRO'llY DRILLING This invention relatesto rock and earth drilling apparatus for rotary drilling which includesan axially stationary, pressure fluid actuated chuck, and an axiallymovable, mechanically rotatable, pressure fluid actuated chuck which isarranged to be moved forward and backward by means of a reversiblepressure fluid driven feed motor. The feed motor has a pressure fluidsupply conduit for each direction. The chucks are arranged toalternately grip a drill string, which is composed of a number of stringelements, so that the drill string can be withdrawn from or inserted ina drill hole by means of the chucks.

A prior form of such adrilling apparatus has a number of manuallyoperated control devices. It is therefor complicated to operate and theoperator must be skilled. It is an object of the invention to create adrill apparatus which has only a few manually operated control devicesso that it will be simple to operate and the net drilling time willtherefore be increased in relation to the gross drilling time.

In connection with the drilling apparatus according to the invention,withdrawing of the drill string from a drill hole and, alternatively,inserting of the drill string in the drill hole are effected by means ofa single manually operated control device because the chucks alternatethe engagement automatically when the axially movable chuck shifts frommoving in one direction to moving in the other. Besides, the drillstring is retained automatically by the chucks if the supply of pressurefluid fails.

For these and other purposes I provide in a drilling apparatus forrotary drilling in rock, the combination of: a frame, a pressure fluidoperated stationary chuck at said frame for gripping a drill string, apressure fluid operated movable chuck for gripping said drill string andslidably carried by said frame, one of said chucks, preferably themovable one, being designed to grip the drill string when loaded bypressure fluid and release if when relieved of fluid pressure. The otherof the chucks is designed to release the drill string when loaded bypressure fluid and grip it when relived of fluid pressure, a motor forrotating said movable chuck, a reversible feed motor for advancing andretracting said movable chuck along the axis of said drill string, afirst supply conduit for supplying pressure fluid to said feed motor foreffecting advance of the movable chuck, a second supply conduit forsupplying pressure fluid to said feed motor for effecting retraction ofthe movable chuck, a supply conduit for supplying pressure fluid to thestationary chuck, a supply conduit for supplying pressure fluid to themovable chuck, and a control which includes a switch, said switch meanshaving a position in which it effects pressurizing of said supplyconduits to the chucks and one of said supply conduits of the feed motorand also having a position in which it effects relief of fluid pressurein said supply conduits of the chucks and said one of the supplyconduits of the feed motor.

The above and other objects of the invention are obvious from thefollowing description and from the accompanying drawings in which apreferred embodiment of the invention is described by way of example.

In the drawings FIG. 1 is a side view, partly in section, of avertically arranged rock and earth drilling apparatus according to theinvention;

FIG. 2 is a front elevation partly in section, of the drilling apparatusillustrated in FIG. 1;

FIG. 3 is an enlarged section on line 3--3 in FIG. 1;

FIG. 4 is an enlarged section on the lines 4-4 in the FIGS. 1 and 5;

FIG. 5 is an enlarged section substantially on line 5-5 in FIG. 1, achuck being illustrated in section on line 5-5 in FIG. 4; and

FIG. 6 is a diagram of the pressure fluid system of the drillingapparatus illustrated in the FIGS. 1-5.

The drilling apparatus illustrated in the FIGS. 1-5 has a feed bar 11which is supported by expanding units 12. Alternatively the feed bar maybe carried by a wheeled substructure or be supported in another suitableway. A slide 13, carries a drill 14, and is slidable along the feed bar11 by means of two parallel chains 15, a chain 16, and a feed motor 17in the form of a cylinder with a reciprocating piston rod 20. The feedmotor 17 has two supply conduits 18, 19. If pressure fluid is suppliedthrough the supply conduit 18, the piston rod 20 retracts and the chain16 pulls the slide 13 forwards, i.e., downwards in FIG. 1. If,alternatively, pressure fluid is supplied through the supply conduit 19,the slide 13 is pulled backwards, i.e., upwards in FIG, 1, by means ofthe chains 15.

A stationary chuck 21 of the vise type is disposed at the forwardportion of the feed bar 11. By means of Belleville springs 24, FIG. 3,its jaws 22 are biased into engagement with a drill string in the formof a drill pipe 23. By the action of pressure fluid upon a piston 240,the force of the springs 24 is overcome and the jaws 22 are forced torelease the drill pipe 23. The pressure fluid is supplied through aconduit 25.

The drill pipe 23 comprises several pipe elements and a drill bit 26which are joined by screw joints. For rock drilling, the drill bit 26may be a pipelike diamond drill bit and the first pipe element may be aso-called core pipe for collecting a core. A swivel 49 supplies flushwater to the drill pipe.

A chuck 27 with a housing 28 is a part of the drill 14, which in FIG. 5is illustrated in a sectional view. This chuck 27 is rotatably joumaledin the housing 29 of the drill 14 by means of a roller bearing 38 and aball bearing 31. Thus, the chuck 27 moves with the drill 14.

A reversible, pressure fluid actuated rotary motor 32 is arranged torotate the chuck 27 over a gearing which comprises gears 33, 34. Thegear 33 is fixed to the output shaft of the rotary motor 32 by means ofa key 35, and the gear 34 is fixed to the housing 28 of the chuck 27 bymeans of another key 35. The rotary motor 32 has two alternative supplyconduits 36, 37. When pressure fluid is supplied through the conduit 36,the motor 32 rotates forward, and when pressure fluid is suppliedthrough the conduit 37, the motor reverses.

Pressure fluid to the chuck 27 is supplied to a passage 40 in thehousing 28 of the chuck by means of a conduit 38 and an annular groove39 in the housing 29. Oil is permitted to leak through an annular gap 41between the rotating chuck 27 and the nonrotating housing 29. This oilis collected and conveyed back to a sump 52 by means of a drain conduit42.

In the chuck housing 28, a sleevelike piston element 43, which hasflanges and is made of an elastomer, is sealingly clamped by means of aspacer sleeve 44 and a cover 45. When pressure fluid is supplied throughthe conduit 38, the piston element 43 forces four jaws 46 of the chuck27 to grip the drill pipe 23. Spring plates 47 are disposed between thejaws 46 to hold the jaws in disengaged position when there is nopressure in the conduit 38. The jaws 46 are guided by guiding pins 48,which transmit torque directly from the housing 28 of the chuck 27 tothe jaws 46 so that the piston element 43 is not subject to torque whenthe chuck is rotated.

In the conduit diagram, FIG. 6, the chucks 21 and 27, the feed motor 17,the rotary motor 32, and the conduits l8, 19, 25, 36, 37, 38, 42 all ofwhich are described above, are represented. The reference numeral 51refers to a pressure fluid supplying unit, which comprises a sump 52 anda pump 53 which is driven by a motor E. Normally, the pressure fluidsupplying unit 51 is situated some distance away from the drillingapparatus. The pump 53 supplies pressure fluid, preferably pressure oil,through a main conduit 54 to a control unit 56, which is indicated bymeans of dash-and-dot lines. Preferably the pump 53 is pressurecompensated, so that it supplies oil of a constant pressureindependently of the amount of oil utilized. By means of a returnconduit 55, oil is returned from the control unit 56 to the sump 52.

A manually operated control valve 57 for the rotary motor 32 is suppliedwith pressure fluid from the main conduit 54. This valve 57, which iscalled the rotation control valve, has three alternative positions which(in FIG. 6) are referred to as positions a, b, and c and represented inFIG. 6 by the corresponding squares a, b, c of the symbol of the valve.With the rotation control valve in position b, as illustrated in theFigure, the conduits 36, 37 are connected to the return conduit 55, and,thus, the rotary motor does not rotate. With the rotation control valve57 in position a, the conduit 36 is supplied with pressure oil from themain conduit 54, and the conduit 37 is drained through the returnconduit 55. Therefore, the rotary motor 32 rotates forward. With thevalve in the position 0, the conduit 36 is drained and the conduit 37 issupplied with pressure oil so that the rotary motor 32 rotates inreverse direction.

The axial movement of the drill 14 is controlled by means of a manuallyoperated control valve 58, which is referred to as the feed controlvalve. This feed control valve 58 has also three positions which arereferred to as a, b, 0. With the feed control valve 58 in position b, asillustrated in the Figure, the two supply conduits 18, 19 of the feedmotor 17 are connected to the return conduit 55, and the drill 14 doesnot move axially. If, simultaneously, the rotation control valve 57 isin position b, the main conduit 54 is directly connected to the returnconduit 55 and the entire drilling apparatus is idling. The feed controlvalve 58 is supplied with pressure oil through a conduit 59independently of the position of the rotation control valve 57. With thefeed control valve 58 in position a, pressure oil is supplied to theconduit 18, and the conduit 19 is connected to the return conduit 55.Thus, the drill l4 advances. With the feed control valve 58 in positionb, pressure oil is supplied to the conduit 19, and the conduit 18 isdrained. Therefore, the drill 14 now retracts.

The supply conduits 25, 38 of the two chucks 21, 27 are branches of acommon supply conduit 60. With a manually operated selector valve 61 ina position a, the supply conduit 18 of the feed motor 17 is connected tothe conduit 60. With the selector valve in a position 0, alternatively,the other supply conduit 19 is connected to the conduit 60. With theselector valve in a position b, the conduit 60 is not connected toeither of the conduits 18, 19. The conduit 38 of the movable chuck 27 isconnected to both of the supply conduits 36, 37 of the rotary motor bymeans of two connection conduits 62, 63. The connection conduits areprovided with one-way valves 64 which permit flow only in the directionof the conduit 38. Between the functions of the connection conduits 62,63 with the conduit 38 and the junction of the conduits 25 with theconduit 38, a one-way restrictor 65 is arranged in the conduit 38. Amanually operated shutoff valve 66 is also arranged in the conduit 38.

An adjustable pressure reducing valve 67 in the conduit 18 sets an upperlimit on the feed power. A manometer 68 indicates the feed pressure.Another manometer 69 indicates the pressure in the main conduit 54. Inthe conduit 19 of the feed motor 17, an adjustable valve 70 of therelief valve type is arranged. This valve closes automatically when thepressure in the conduit 19 is lower than a predetermined pressure. Thepurposes of this valve 70 are to compensate for the weight of the drill14 and the drill pipe 23 during drilling and to prevent the drill withthe drill string to move downward because of the weight only. A one-wayvalve 71 is connected in parallel with the valve 70, and retraction ofthe drill 14 is permitted. When drilling upward is to be eifected, thevalves 70, 71 are connected in the conduit 18 instead of the conduit 19.

For effecting idle run, both the rotation control valve 57 and the feedcontrol valve 58 are set in the neutral positions, i.e., the positionsb. The drill pipe 23 is then held by the stationary chuck 21. Whendrilling is to be started, at first the selector valve 61 is set intoposition b, then, the rotation control valve 57 is moved into positiona. Now, pressure oil flows through the connection conduit 62 to thechucks 21 and 27 so that simultaneously, the chuck 27 grips with thedrill pipe, the chuck 21 releases the drill pipe, and the chuck 27begins to rotate. Now, when the feed control valve 58 is moved toposition a, the drill 14 advances. The advance stops automatically whenthe piston rod 20 of the feed motor 17 reaches its retracted stopposition provided the feed control valve 58 is not shifted before thisposition is reached.

When the rotation control valve 57 is reset into the position b, thechucks 21, 27 alternate the engagement and another pipe element can bemanually screwed on to the drill pipe 23. Thereafter the swivel 49 isscrewed on to the end of the drill pipe 23. When the feed control valve58 is moved into position 0, the drill 14 is returned to its retractedposition which is defined by the extended stop position of the pistonrod 20 of the feed motor 17. The drilling starts again when the rotationcontrol valve 57 and the feed control valve 58 are set in the positionsa.

For withdrawing of the drill pipe 23, the selector valve 61 is set inposition 0, and the rotation control valve 57 in position b. The feedcontrol valve 58 is now used as a common control valve for the twochucks 21, 27 and the feed motor 17. When the feed control valve 58 ismoved from position b, the neutral position, to the position 0, thechuck 21 releases the drill pipe, but the chuck 27 grips the drill pipe,and withdraws it. When the feed control valve 58 is moved into positiona, the chucks alternate engagement automatically, and the drill 14advances without pushing the drill pipe forward. This is repeated, ifnecessary, until the drill pipe is withdrawn an appropriate length.Then, the feed control valve 58 is moved to the position b, the neutralposition, and the rotation control valve 57 is moved to the position c.Now, the chuck 27 rotates in reverse direction and the supply conduit60, common to the two chucks 21, 27, is drained through the selectorvalve 61 and the feed control valve 58. Through the connection conduit62, however, the movable chuck 27 is supplied with pressure oil. Onaccount of the restrictor 65, there is oil pressure on this chuck 27,and the chuck 27 grips the drill pipe. The stationary chuck 21,maintains its grip since the flow through the restriction valve isdrained through the common supply conduit 60 of the chucks 21, 27.Therefore, if there is a screw joint of the drill rod between thechucks, this joint will be broken mechanically when the control valves57, 58 are in these positions. In order to facilitate breaking of verytight joints, the stationary chuck 21 may be rotatable a limited angle,e.g., an angle of 25 so that an impact results.

When it is desired to reinsert the drill pipe in the drill hole, theselector valve 61 is set in position a. The movable chuck 27 will nowbring the drill pipe 23 forward when the drill 14 advances, and thestationary chuck 21 will hold the drill pipe during retraction of thedrill. With the rotation control valve 57 maintained in the position b,the neutral position, this reinsertion is controlled by means of thefeed control valve 58. When the drill pipe 23 has been introduced so farthat the stationary chuck 21 holds the outer end of the pipe, anotherpipe element is manually screwed on loosely, and the drill 14 isretracted. Then the rotation control valve 57 is moved to the positiona. As a result, the movable chuck 27 engages and rotates the pipeelement, while the stationary chuck 21 holds the drill pipe 23 becauseof the restriction valve 65 which is the case also during breaking ofjoints. Thus, the joint is made. Then, the drill pipe 23 is againinserted so far that the chuck 21 will again hold the outer end of thedrill pipe, and the sequence is repeated.

In order to permit inserting of the drill bit and the first drillpipeelement through the two chucks 21, 27, the chucks must be opensimultaneously. For this purpose, the operator closes the shutoff valve66, sets the rotary control valve 57 in the position b, the neutralposition, and sets the selector valve 61 and the feed control valve 58in the position a. As a result, the drill 14 advances until it stops inits advanced stop position. The two chucks 21, 22 are now open.Alternatively, the selector valve 61 and the feed control valve 58 canbe set in the position 0 so that the drill 14 stops in its retractedstop position.

In connection with the drilling apparatus described above, the twochucks 21, 27 are thus controlled automatically. During drilling andduring making and breaking of joints, the controlling of the chucks isaccomplished by means of the control valve 57 of the rotary motor, and,during introducing of and withdrawing of the drill string, it iseffected by means of the control valve 58 of the feed motor.

Especially in connection with large drilling apparatus, it can bedesirable to drill with a relatively high rotary speed in hand rocks; alower rotary speed and a higher torque is required for earth drillingand drilling in soft rocks and for making and breaking joints. For thispurpose, a two speed gear box (nonillustrated) may be operationallyconnnected between the rotary motor 32 and the chuck 27 so that twodifferent rates of transmission between the motor and chuck areachieved. In

connection with a modified nonillustrated design, the axial power andthe torque is transmitted by means of a releasable clutch duringdrilling in hard rocks. This clutch is mounted at the back portion ofthe drill M and adapted to be screwed to the back end of the drillstring. This clutch is rotated, over a gearing, with a higher speed thanthe chuck 27, which is prevented from engagement with the drill stringwhen the shutoff valve as is closed. in connection with this modifieddesign, the drill string is rotated by means of the chuck 27 with thelower speed higher torque only during the operations of making andbreaking joints and drilling in soft rocks and earth.

The invention is not limited to the described embodiments, but may bemodified in various ways within the scope of the claims.

1 claim:

ll. in a drilling apparatus for rotary drilling in rock, the combinationof: a frame, a pressure fluid operated stationary chuck at said framefor gripping a drill string, a pressure fluid operated movable chuck forgripping said drill string said movable chuck being slidably carried bysaid frame, one of said chucks, preferably the movable one, beingdesigned to grip the drill string when loaded by pressure fluid andrelease it when relieved of fluid pressure and the other of the chucksbeing designed to release the drill string when loaded by pres surefluid and grip it when relieved of fluid pressure, a motor for rotatingsaid movable chuck, a reversible feed motor for advancing and retractingsaid movable chuck along the axis of said drill string, a first supplyconduit for supplying pressure fluid to said feed motor for effectingadvance of the movable chuck, a second supply conduit for supplyingpressure fluid to said feed motor for effecting retraction of themovable chuck, a supply conduit for supplying pressure fluid to thestationary chuck, a supply conduit for supplying pressure fluid to themovable chuck, and a control means which includes a switch means, saidswitch means having a position in which it effects pressurizing of saidsupply conduits of the chucks and one of said supply conduits of thefeed motor and also having a position in which it effects relief offluid pressure in said supply conduits of the chucks and said one of thesupply conduits of the feed motor.

2. A drilling apparatus according to claim 11 further comprising aselector valve which, when in a position for inserting of the drillstring into a drill hole, connects the supply conduits of the two chucksto said first supply conduit of the feed motor, and which, when in aposition for withdrawing of the drill string, connects the supplyconduits of the two chucks to said second of the two supply conduits ofthe feed motor, said switch means being a valve which has a position inwhich it connects said first supply conduit of the feed motor to asource of pressure fluid and the second supply conduit of the feed motorto a sump, and which has a position in which it connects said firstsupply conduit of the feed motor to the sump and the second supplyconduit of the feed motor to the source of pressure fluid.

3. A drilling apparatus according to claim 2 in which said selectorvalve has a third position in which it blocks off the supply conduits ofthe chucks from both of the supply conduits of the feed motor, thisthird position being the position of the selector valve during drilling.

4. A drilling apparatus according to claim 2 in which the supplyconduits of the chucks are branches from a common supply conduit inwhich said selector valve is arranged.

5. A drilling apparatus according to claim 4 in which the axiallymovable chuck is the chuck which grips the drill string when loaded bypressure fluid, the motor for rotating the movable chuck is a pressurefluid driven reversible rotary motor with two alternative supplyconduits, and the supply conduit of the axially movable chuck isconnected to each of the supply conduits of the rotary motor by means ofconnection conduits which include one-way valves which permit flow onlyin the direction towards the supply conduit of the chuck.

6. A drilling apparatus according to claim 5 in which said common supplyconduit of the chucks is drained when the drilling apparatus is adaptedfor making joints and when adapted for breaking joints, and arestriction is arranged in the supply conduit of the movable chuckbetween the junctions of said connection conduits with the supplyconduit of the movable chuck and the junction of said common supplyconduit of the chucks with the supply conduit of the movable chuck sothat, when the rotary motor is caused to rotate by pressure fluid beingsupplied through either of its supply conduits, pressure is maintainedin the supply conduit of the movable chuck but the supply conduit of thestationary chuck is maintained substantially relieved of pressure.

7. A drilling apparatus according to claim 1 in which the jaws of thestationary chuck are spring-biased into gripping engagement with thedrill string.

8. A rock drilling apparatus for rotary drilling comprising a frame, afirst chuck having jaws, said jaws being spring-biased to grip a drillstring, a first piston means which, when loaded by pressure fluid,causes said jaws to release the drill string, a second chuck having jawswhich are biased to release said drill string, a second piston meanswhich, when loaded by pressure fluid, causes the jaws of said secondchuck to grip the drill string, one of said chucks being fixed to theframe, the other chuck being axially movably carried by said frame, asupply conduit for supplying pressure fluid to the first piston means, asupply conduit for supplying pressure fluid to said second piston means,said supply conduits being branches of a common supply conduitcontrolled by a valve which has a first position in which it connectssaid common supply conduit to a source of pressure fluid and which valvehas a second position in which it connects said common supply conduit toa relief conduit.

1. In a drilling apparatus for rotary drilling in rock, the combinationof: a frame, a pressure fluid operated stationary chuck at said framefor gripping a drill string, a pressure fluid operated movable chuck forgripping said drill string said movable chuck being slidably carried bysaid frame, one of said chucks, preferably the movable one, beingdesigned to grip the drill string when loaded by pressure fluid andrelease it when relieved of fluid pressure and the other of the chucksbeing designed to release the drill string when loaded by pressure fluidand grip it when relieved of fluid pressure, a motor for rotating saidmovable chuck, a reversible feed motor for advancing and retracting saidmovable chuck along the axis of said drill string, a first supplyconduit for supplying pressure fluid to said feed motor for effectingadvance of the movable chuck, a second supply conduit for supplyingpressure fluid to said feed motor for effecting retraction of themovable chuck, a supply conduit for supplying pressure fluid to thestationary chuck, a supply conduit for supplying pressure fluid to themovable chuck, and a control means which includes a switch means, saidswitch means having a position in which it effects pressurizing of saidsupply conduits of the chucks and one of said supply conduits of thefeed motor and also having a position in which it effects relief offluid pressure in said supply conduits of the chucks and said one of thesupply conduits of the feed motor.
 2. A drilling apparatus according toclaim 1 further comprising a selector valve which, when in a positionfor inserting of the drill string into a drill hole, connects the supplyconduits of the two chucks to said first supply conduit of the feedmotor, and which, when in a position for withdrawing of the drillstring, connects the supply conduits of the two chucks to said second ofthe two supply conduits of the feed motor, said switch means being avalve which has a position in which it connects said first supplyconduit of the feed motor to a source of pressure fluid and the secondsupply conduit of the feed motor to a sump, and which has a position inwhich it connects said first supply conduit of the feed motor to thesump and the second supply conduit of the feed motor to the source ofpressure fluid.
 3. A drilling apparatus according to claim 2 in whichsaid selector valve has a third position in which it blocks off thesupply conduits of the chucks from both of the supply conduits of thefeed motor, this third position being the position of the selector valveduring drilling.
 4. A drilling apparatus according to claim 2 in whichthe supply conduits of the chucks are branches from a common supplyconduit in which said selector valve is arranged.
 5. A drillingapparatus according to claim 4 in which the axially movable chuck is thechuck which grips the drill string when loaded by pressure fluid, themotor for rotating the movable chuck is a pressure fluid drivenreversible rotary motor with two alternative supply conduits, and thesupply conduit of the axially movable chuck is connected to each of thesupply conduits of the rotary motor by means of connection conduitswhich include one-way valves which permit flow only in the directiontowards the supply conduit of the chuck.
 6. A drilling apparatusaccording to claim 5 in which said common supply conduit of the chucksis drained when the drilling apparatus is adapted for making joints andwhen adapted for breaking joints, and a restriction is arranged in thesupply conduit of the movable chuck between the junctions of saidconnection conduits with the supply conduit of the movable chuck and thejunction of said common supply conduit of the chucks with the supplyconduit of the movable chuck so that, when the rotary motor is caused torotate by pressure fluid being supplied through either of its supplyconduits, pressure is maintained in the supply conduit of the movablechuck but the supply conduit of the stationary chuck is maintaInedsubstantially relieved of pressure.
 7. A drilling apparatus according toclaim 1 in which the jaws of the stationary chuck are spring-biased intogripping engagement with the drill string.
 8. A rock drilling apparatusfor rotary drilling comprising a frame, a first chuck having jaws, saidjaws being spring-biased to grip a drill string, a first piston meanswhich, when loaded by pressure fluid, causes said jaws to release thedrill string, a second chuck having jaws which are biased to releasesaid drill string, a second piston means which, when loaded by pressurefluid, causes the jaws of said second chuck to grip the drill string,one of said chucks being fixed to the frame, the other chuck beingaxially movably carried by said frame, a supply conduit for supplyingpressure fluid to the first piston means, a supply conduit for supplyingpressure fluid to said second piston means, said supply conduits beingbranches of a common supply conduit controlled by a valve which has afirst position in which it connects said common supply conduit to asource of pressure fluid and which valve has a second position in whichit connects said common supply conduit to a relief conduit.